Athletic playing fields such as football and soccer fields or running tracks are typically provided with an artificial surface formed of a resilient and wearable material. In particular, a running track surface may include a polymeric surface layer which is substantially impervious to liquids. Accordingly, a running track surface is often provided with a drainage channel along an edge of the track surface for receiving and collecting liquid runoff. Another running track surface or another type of athletic surface, such as an artificial turf surface or a natural grass surface, may be positioned adjacent to the opposite side of the drainage channel. These other athletic surfaces may also require drainage and, in some instances, may be slightly crowned or sloped from the center to the edges to ensure proper drainage into the adjacent channel.
In forming an athletic playing surface adjacent to a drainage channel, a variety of subsurface layers are built up against the channel to a predetermined level such that a surface layer, which typically has a predetermined thickness, will have an exposed upper surface which is at a desired level. For example, for running track surfaces, an asphalt layer, which may or may not be porous, is applied over an underlying gravel layer to a predetermined elevation. A relatively thin running track surface is then formed over the asphalt layer such that the uppermost surface of the running track surface is at the desired horizontal elevation.
Such a running track surface is typically formed by pouring a moldable material, such as a urethane polymer, adjacent to the drainage channel and allowing the material to cure, thereby forming a resilient surface layer. Because the moldable material is applied in a substantially liquid form, it is desirable that the moldable material be restrained during formation so that the resulting track surface has a well-defined edge after the material has cured.
With conventional running track surfaces, the desired level of the upper exposed surface of the surface layer is often at or below the upper surface of the channel sidewall. Accordingly, the sidewall of the channel acts as a dam to restrain the moldable material while it cures. However, in these instances, the relatively hard upper surface of the drainage channel will generally be exposed to the surface, thereby creating a potential safety hazard for athletes and others.
For some athletic playing surfaces, it is desirable to form the underlying asphalt layer to an elevation corresponding to an upper surface of the sidewall of the channel. Accordingly, the running track surface will typically be formed above the upper surface of the sidewall to the desired thickness. As will be apparant to those skilled in the art, the sidewalls of the drainage channel can no longer serve as a dam during the formation of a running track surface above the upper surface of the sidewall, thereby significantly complicating the running track formation process.
For other athletic surfaces, however, a thinner running track surface is desired in order to reduce the overall cost of the athletic playing field even though the upper surface of the running track is preferably maintained at the same elevation as before. In such situations, a thicker asphalt layer is generally applied over the underlying gravel layer to an elevation slightly higher than the upper surface of the sidewall. Moldable material may then be applied over the thicker asphalt layer to the same elevation as before, thereby resulting in a thinner and less costly surface layer. As described above, however, the process of forming both the asphalt layer and the surface layer is significantly complicated since the sidewalls of the drainage channel can no longer serve as a dam for surfaces formed above the upper surface of the sidewall.
For artificial turf surfaces, the asphalt layer is typically thinner than the asphalt layer described above so that a layer of cushioning foam and the artificial turf may be applied thereover to provide an uppermost surface at the desired level. However, the subsurface layers should still be applied to the proper elevation relative to the drainage channel so that the uppermost exposed surface of the playing surface is located at the proper elevation.
Regardless of the type of athletic surface bordering the drainage channel, an elongate grate is typically provided over the drainage channel so as to cover the open top of the channel in order to prevent people from unwittingly stepping into the open channel and/or to prevent relatively large objects from entering the channel and partially blocking the flow of liquid therethrough. While the grate effectively covers the open top of the drainage channel, the drainage system and, in particular, the portion of the grate which is exposed to the surface can decrease the aesthetic appeal of the athletic playing fields. Since the drainage channel commonly extends along or between athletic surfaces over which a number of people and vehicles will be passing, it is desirable for the drainage channel and, more particularly, the grate to be free of upstanding protrusions. In addition, because the grate is substantially rigid, it is desirable that the grate be cushioned relative to the channel in response to downward loading forces applied to the grate, such as a falling athlete.
A system of grate edging is commercially available under the trademark Aco Sport.RTM. from Aco Polymer Products, Inc. to border natural grass surfaces, artificial turf surfaces and/or running track surfaces. The Aco Sport.RTM. system includes a number of drainage channel configurations which, in some embodiments, are covered by a variety of grates and/or a polymer concrete hard cover. A number of the Aco Sport.RTM. drainage systems include a border or curb formed of ethylene-propylene diene monomer ("EPDM") which delineates the boundary between the adjacent athletic surfaces. Due to the upwardly extending EPDM border, athletes or others must step over the EPDM border to pass over the EPDM border and between the adjacent athletic surfaces. In addition, athletic surfaces which border the Aco Sport.RTM. drainage system are also typically at different elevations so as to create an additional barrier to passing between the athletic playing surfaces.
U.S. Pat. No. 4,553,874 to Thomann et al. describes another type of drainage system. In particular, Thomann et al. discloses a slotted grate intended to fit within a preformed cast drainage channel section. The channel section includes a drainage channel body and a cast frame supported thereon for supporting the channel grate. The channel body may be manufactured of polymer concrete and is provided with protrusions on each side to firmly anchor the drainage channel body within a concrete foundation, which encases most of the channel body. Guide tabs on the cast frame intermesh with a pavement layer which may be formed over the concrete.
As described above, several drainage systems, including the Aco Sport.RTM. drainage system, have been developed which border athletic playing surfaces in order to receive runoff therefrom. However, these drainage systems still do not fully address the needs of modern athletic playing surfaces. For example, the prior drainage systems do not define an edge of a polymer athletic surface, such as a running track, or a subsurface layer formed adjacent to the drainage channel and above the uppermost portion of the drainage channel sidewall. Further, at least some of these prior drainage systems do not maintain the athletic playing surfaces which are adjacent to the opposed sides of the drainage channel in a level orientation in order permit athletes and others to more readily pass thereover.